1. Field of the Invention
This invention relates generally to valves used in a heating system. More particularly, the present invention relates to a valve actuating device for a zone heating and/or cooling system which is both opened and closed by a D.C. motor.
2. Discussion of the Related Art
In zone heating and/or cooling systems, valves are provided for controlling the flow of heated or cooled fluid (e.g., water or coolant) to the zones they service. One type of valve well-known in the heating and cooling industry is a heat motor type valve which utilizes wax as a pressure medium for opening and closing a valve member. More particularly, wax, in its hardened state, is softened by suitable heating means for moving the valve member of the valve from its closed to its opened position. This type of valve is desirous in circumstances where the valve needs to be opened slowly to prevent water hammer in the system. Water hammer is caused by opening or closing a valve too quickly in a system thereby causing a pressure wave which moves back and forth within the system until the pressure wave comes into contact with another valve or an end of a particular branch of the system. However, the heat motor valve suffers from the limitation that it takes too long to heat the wax and therefore too long to open and close the valve member. Typically, such a valve takes approximately four minutes to open and six minutes to close. Contractors installing a heating and/or cooling system find the waiting period between the opening and closing of the valve too long to adequately test the valve after it has been installed in the system. Although the performance of such valves is not suspect, the waiting period causes many contractors to avoid using this type of valve.
As an alternative to the heat motor type valve, another valve available to contractors is actuated by a solenoid switch which immediately introduces or cuts-off fluid to the system. However, this valve has been known to cause water hammer since it opens and closes the valve too quickly. There is presently a need for a valve which does not open and close immediately as the solenoid switch actuated valve and takes less time to open and close than the heat motor type valve.
Reference can be made to U.S. Pat. No. 5,529,282 to Lebkuchner, which is assigned to the assignee of the present application, as a solution to the foregoing problems associated with the prior art. More specifically, this patent discloses a valve actuating device comprising a housing having a fitting which is threadably received by a fitting receiving formation of a valve for securing the housing to the valve. The device further includes an electric motor mounted on the housing, the motor being adapted to drive a shaft having a pinion gear upon its activation for opening the valve. A rack has teeth engageable with the pinion gear of the electric motor and an end portion engageable with a valve stem of the valve. The arrangement is such that the rack is movable upon activation of the motor from a first position in which the end portion of the rack engages the valve stem for maintaining the valve stem in its closed position against the bias of valve stem biasing means (e.g., a spring), to a second position in which, upon activation of the motor, the rack is moved via the pinion gear of the motor away from the valve stem thereby enabling the valve stem biasing means to move the valve member to its open position. Two springs bias the rack to its first position.
While certainly effective for its intended purpose, since the actuator device disclosed in the Lebkuchner patent must continuously energize the motor in order to maintain the valve in the open position. This puts undue stress on the motor and therefore shortens the life of the motor. Furthermore, due to the design of the Lebkuchner device, the valve can only be fully open or fully closed. The device does not allow the valve to be held partially open in order to modulate the flow of fluid through the valve.